Steel alloy blanks for glass-to-metal seal



United States Patent STEEL ALLOY BLANK]? FOR GLASS-TO-METAL S AL Freeman J. Phillips and Raymond Smith, Pittsburgh, Pa., assignors to United States Steel Corporation, a corpora tion of New Jersey No Drawing. Application September 12, 1951, Serial No. 246,334

2 Claims. (Cl. 75-126) This invention relates to a steel of novel composition having a coeflicient of thermal expansion which renders it suitable for making metal-to-glass seals.

Certain modern industrial applications of metal-to-glass seals present a problem of considerable difficulty. One of these is the kinescope or television screen tube which usually comprises a metal cone, a glass disc overlying the large end thereof and a glass tube aflixed coaxially to the small end. For such an application, the metal of which the cone is composed must have a thermal coeflicient of expansion such that a Wide variation in temperature, i. e., from about 2190 F., the temperature at which the seal is formed, to room temperature, will not fracture the glass as a result of differential contraction. After completion of the seal, furthermore, the glass portion thereof must not show substantial residual strain since such strain, if excessive, increases the danger of breakage by the shock or impact incident to handling and shipping. The metal, moreover, must have sufficient ductility to permit spinning the cone-shaped body of the tube from a piece of flat sheet. While certain known alloys have substantially the same coefiicient of thermal expansion as the glass used to form the disc and small end of the tube, e. g., about 11 10- in./in./C., they cannot be formed as by spinning. Conversely, conventional steels having the requisite spinning quality cannot be employed because they oxidize too readily and have thermal coefiicients difiering too widely from that of the glass used for the receiving end of the tube.

We have discovered a novel ferrous alloy which satisfactorily meets all the requirements of the trade in respect to producing a glass-to-metal seal.

We have discovered that, in order to meet these requirements, not only must the composition of the steel be closely controlled to render it completely ferritic at sealing temperatures as high as 2190 F. (1200 C.) but the compositional ranges must be closely controlled to produce steel having a proper coelficient of expansion over the full range between room temperature and the foregoing sealing temperature of glass. To attain this desirable condition, the steel should have a coefiicient of expansion very closely approximating that of the glass being utilized. We have further found that such conditions can be achieved by closely balancing the amount of carbon, chromium, manganese, nickel, silicon, aluminum and titanium as more fully described hereinafter within the following limits:

Sulphur maximum, .04

We have determined that meeting the foregoing requirement of being fully ferritic, requires proper balancing of the amount of the austenite formers, nickel, manganese and carbon with respect to the ferrite formers, chromium, silicon, titanium and aluminum. A fully ferritic steel can be obtained if the elements are properly balanced and restricted to amounts consistent with the following Formula A to obtain a sum which is greater than unity, i. e., a positive value ascontrasted to a negative result which indicates a two-phased or unsatisfactory steel.

Formula A Percent Cr+percent Si/2+30 percent Ti+10 percent Al4.27(percent Ni-l-percent Mn/2+30Xpercent C)-19.56=a positive or negative value For example, a heat containing .06% carbon, .50'% manganese, 016% phosphorus, .009% sulphur, 33% silicon, .13% nickel, 17.78% chromium, 46% titanium and .06% aluminum was fully ferritic as is shown by application of the foregoing formula:

i. e., a fully ferritic steel.

On the other hand, application of the formula shows the following steel containing .07% carbon, .55 manganese, 30% silicon, .l0% nickel, 17.36% chromium, 31% titanium, 06% aluminum to be unsatisfactory:

i. e., a two-phased and unsatisfactory steel.

We have further discovered that being fully ferritic does not necessarily result in the steel having desired coefficient of expansion. We have determined that silicon, aluminum and manganese additions to a substantially 17% chromium steel increase the coefficient of expansion Whereas nickel, chromium and titanium decrease the coeflicient of expansion. These elements can be properly balanced to produce the desired coefficient of expansion. For example, if it is desired to control the coefficient of expansion to less than 11.7 at temperatures between 986 F. (530 C.) and 36 F. (30 C.), the amounts of the elements should be restricted in accordance with the following Formula B. The numerical values thereof can of course be varied if it is desired to control the coefiicient over difierent ranges of temperatures.

Formula "B 12.29l7+.0667(% Mn) +.2307(% Si) +.2487(% Al) .0448(% Ni) .0484( Cr) -.0399(% Ti) X 10- Coefiicient of expansion in./in./ C.

For example, where the usage of the material necessitates a coeflicient of expansion less than 11.7 in./in.C., application of the foregoing formula determines that a steel containing .06% carbon, 1.05% manganese, 1.02% silicon, 1.06% nickel, 17.22% chromium, .60% titanium and 1.07% aluminum has a coefficient of 11.96 in./in./ C. and is therefore unsatisfactory. However, a steel containing .068% carbon, 1.11% manganese, 36% silicon, .57% nickel, 18.06% chromium, 52% titanium and .19% aluminum is shown to have a coefficient of expansion of 11.58 and is therefore satisfactory.

Requirements of the foregoing formulae can ordinarily be attained by limiting the compositional ranges to the following preferred embodiment of our invention:

If desired to further lower the coefiicient of expansion, other elements such as columbiurn, molybdenum, tungsten and vanadium may be added in amounts up to 1.0% each and boron up to 006%.

a This application is a contmuation-iu-part of our copending application Serial No. 140,955, filed January 27,

1950, now Patent No. 2,672,414, issued March 16, 1954 and application Serial No. 123,899, filed October 27, 1949, now abandoned.

While We have shown and described several specific embodiments of our invention, it will be understood that these embodiments are merely for the purpose of illustration and description and that various other forms may be devised Within the scope of our invention, as defined in the appended claims.

We claim:

1. A metal blank for forming a glass-to-metal seal, said blank being formed of steel containing .005 to .12% carbon, to chromium, nil to 1.00% manganese, nil to 1.00% silicon, nil to 1.00% aluminum, about .40% to 1.00% titanium, nil to 1.00% nickel, and balance substantially iron, said carbon, chromium, silicon, aluminum, titanium, manganese and nickel being restricted to amounts consistent with the formula Percent Cr-l-percent Si/2+30 percent Ti+10 percent Al4.27(percent Ni-l-percent Mn/2-l-30Xpercent C) 19.56=a numerical value greater than unity and said chromium, silicon, aluminum, titanium, manganese, and nickel being further restricted to amounts consistent with the formula 12.29l7+.0667(percent Mn)+.2307(percent Si)+.2487 (percent Al).0448(percent Ni)-.0484(percent Cr).0399(percent Ti)=a numerical coefficient value less than 11.7 10" in./in./C. at temperatures between 30 and 530 C.

2. A metal blank for forming a glass-tometal seal, said blank being formed of steel containing .005 to .12% carbon, 15 to 20% chromium, nil to 1.00% manganese, nil to 1.00% silicon, nil to 1.00% aluminum, nil to 1.00% titanium, nil to 1.00% nickel, and balance substantially iron, said carbon, chromium, silicon, aluminum, titanium, manganese and nickel being restricted to amounts consistent with the formula Percent Cr+percent Si/2-l-30Xpercent Ti+10 percent Al4.27(percent Ni+percent Mn/2+30Xpercent C)19.56=a numerical Value greater than unity said steel being characterized by being completely ferritic after quenching from 2190" F.

References Cited in the file of this patent UNITED STATES PATENTS 1,464,312 Fahrenwald Aug. 7, 1923 1,850,953 Armstrong Mar. 22, 1932 1,947,417 Holst Feb. 13, 1934 2,024,561 Becket et a1. Dec. 17, 1935 2,603,177 Gardiner July 15, 1952 OTHER REFERENCES Alloys of Iron and Chromium, High Chromium, vol. II, pages 88 and 89. Edited by Kinzel. Pub. in 1940 by McGraw-Hill Book Co.

Metal Progress, June 1950, pages 761 to 764, inclusive. 

2. A METHOD BLANK FOR FORMING A GLASS-TO METAL SEAL, SAID BLANK BEING FORMED OF STEEL CONTAINING .005 TO .12% CARBON, 15 TO 20% CHROMIUM, NIL TO 1.00% MANGANESE, NIL TO 1.00% NIL TO 1.00% ALUMINUM, NIL TO 1.00% TITANIUM, NIL TO 1.00% NICKEL, AND BALANCE SUBSTANTIALLY IRON, SAID CARBON, CHROMIUM, SILICON, ALUMINUM, TITANIUM, MANGANESE AND NICKEL BEING RESTRICTED TO AMOUNTS CONSISTENT WITH THE FORMULA 